Wavelet analysis of autonomic outflow of normal subjects on head‐up tilt, cold pressor test, Valsalva manoeuvre and deep breathing

Abstract

Non-invasive autonomic evaluation has used fast Fourier transform (FFT) to assign a range of low (LF) and high frequencies (HF) as markers of sympathetic and parasympathetic influences, respectively. However, FFT cannot be applied to brief transient phenomena, such as those observed on performing autonomic tests where the acute changes of cardiovascular signals (blood pressure and heart rate) that represent the first and most important stage of the autonomic performance towards a new state of equilibrium occur. Wavelet analysis has been proposed as a method to overcome and complement information taken exclusively in the frequency domain. With discrete wavelet transform (DWT), a time-frequency analysis can be done, allowing the visualization in time of the contribution of LF and HF to the observed changes of a particular signal. In this study, we evaluate with wavelets the acute changes in R-R intervals and systolic blood pressure that are observed in normal subjects during four classical autonomic tests: headup tilt (HUT), cold pressor test (CPT), deep breathing (DB) and Valsalva manoeuvre (VM). Continuous monitoring of ECG and blood presure was performed. Also LF, HF and LF/HF were calculated. Consistent with previous interpretations, data showed an increase of sympathetic activity in HUT, CPT and VM. On DB, results reflected an increase in parasympathetic activity and frequencies. In conclusion, when compared with FFT, wavelet analysis allows the evaluation of autonomic variability during short and non-stationary periods of time and may constitute a useful advance in the assessment of autonomic function in both physiological and pathological conditions.

Consciously Controlled Breathing Decreases the High-Frequency Component of Heart Rate Variability by Inhibiting Cardiac Parasympathetic Nerve Activity

“…After a 5-min rest for stabilization, they were asked to consciously control their breathing to 6 and 15 breaths/min (0.10 and 0.25 Hz) for 5 min at random using a digital timer following spontaneous breathing without conscious control for 5 min. The breathing rate of 6 breaths/min was selected as it could induce dynamic changes in f and V T during the transition from spontaneous to consciously controlled breathing and has been frequently used to investigate the influence of slow and deep breathing on the ANS (Hayano et al 1994;Pitzalis et al 1998;Ducla-Soares et al 2007). The breathing rate of 15 breaths/min is close to the mean respiratory rate in adults and has been often used to standardize measurements obtained in spectral analysis of HRV (Brown et al 1993;Bernardi et al 2000;Piccirillo et al 2004).…”

Hormonal and autonomic responses to autonomic stimulation are altered in young men with Down syndrome

“…The cold pressor test aims to increase systolic blood pressure during immersion [27,28]. In our study SBP and DBP increased in both groups attesting of an appropriate pressor response to immersion.…”

Reliability of a wearable system to evaluate ambulatory autonomic activity

“…For that, the subject was instructed to breath, for a period of 15s, against a pressure of 40 mmHg after a deep inspiration. After this manoeuvre, a final rest period of 3 min was allowed to elapse before the same subject was instructed to breathe deeply at a rate of 6 breaths min −1 , guided by a metronome, for a period of 1 min, as stated elsewhere [4] . Temperature, respiratory rate and heart beat were continuously acquired through the T-shirt sensors.…”